PAGE one OF FOUR 3 ), 4 ), 4 and 2 ) 3 ), sulfate (MgSO 2 ). 3 ] and carbonate compounds (CaCO 2 ) is the most common source of 3 2 Noncarbonate hardness is the portion of cal- cium and magnesium present as noncarbonate salts, such as calcium sulfate (CaSO and MgCO chloride (CaCl noncarbonate hardness. Carbonate hardness is the portion of total hardness present in the form of salts [Ca(HCO and magnesium chloride (MgCl). The sum of carbonate and noncarbonate hardness equals total hardness. Mg(HCO

○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ ○○○○○○○○○○○○ A NATIONAL DRINKING WATER CLEARINGHOUSE FACT SHEET FACT CLEARINGHOUSE DRINKING WATER A NATIONAL ) or liquid CO 2 ] or quicklime (CaO) may be used in the softening process. The ] or quicklime (CaO) may be used ). Total hardness 2 3

for recarbonation. can also be differentiated into carbonate and NATIONAL DRINKING WATER CLEARINGHOUSE DRINKING WATER NATIONAL What is ? is hard What “Hardness” in water is primarily the result of concentrations of calcium and magnesium. Thus, some water utilities remove calcium and magnesium to soften the water and improve its quality for domestic use. Other ions that pro- duce hardness include , manganese, strontium, barium, zinc, and aluminum, but these ions are generally not present in signifi- cant quantities. Therefore, total hardness is usually defined as the sum of magnesium and calcium hardness in milligrams per liter (mg/L), as (CaCO Hard scaling problems water can cause does not lather well in in water heaters and soap Therefore, water to improve some water utilities soften its quality for domestic hard water. is best suited to groundwateruse. Lime softening sources, have relatively stable water which and the complexity of the chemistry of variable source water quality quality. The combination too complex for small systems that use surfaceof lime softening may make lime softening water sources. used successfully by groundwater systems serving fewer Although lime softening has been be suitable for treatingthan 3,000 people, it is unlikely to groundwater in systems serving have some form500 or fewer people unless those systems of contract or satellite operation to monitor the treatment process.that would enable a trained operator Prefabricated lime Works small systems. Also, theresoftening equipment is available for is an American Water B202-93) that provides Association Standard hydrated lime (ANSI/AWWA for quicklime and purchasers, manufacturers, and suppliers with the minimum requirements, including and testing requirements.physical, chemical, packaging, shipping, Either hydrated lime [Ca(OH) Summary choice depends upon economic factors, such as the relative cost per ton of the two materials choice depends upon economic factors, of the softening plant. Hydrated lime is generally used as well as the size and equipment storesmore in smaller plants because it better and does not require slaking (producing a it with water) equipment. On the other hand, quick- chemical change in lime by combining calcium oxide and is thus more economical for use in lime costs less per ton of available large plants. and scale-formationSoftened water has high causticity potential; hence, recarbonation is scaling of downstreamemployed to reduce pH and mitigate processes and pipelines. Onsite combustion generation of carbon dioxide (CO Lime Softening Lime two

PAGE OF FOUR Lime Softening Induced draft oropentrayaerationis often calciumcarbonateresiduals. and increased to operationcostsbecause ofchemicalexpenses wateradds ofcarbondioxideinsource removal high.Lime relatively dioxide concentrationsare carbon only applicabletogroundwaters where waterbeforesoftening.Thisis thesource from Aeration aerationandpresedimentation. lime softeningare usedbefore The principaltypesofpretreatment What pretreatment isused? with variablequality. watersources pilot testedifusedonsurface quality. Lime-softeningsystemsdoneedtobe waterthatchangesin infiltration bysurface issubjecttoperiodic unless thegroundwater overtime chemicals shouldnotchangegreatly Dosesofthese chemical dosesissufficient. pHand appropriateprocess to determine Jartesting sources. systems usinggroundwater systems neednotbepilottestedforsmall ing needstobecloser11.Lime-softening thepHduringsoften- isalso required, removal bonate, essentiallylimestone.Ifmagnesium 10.Thisremovescalciumcar- approximately hydrated limetorawwaterraisethepH softening istypicallypracticedbyadding is between6.5–8.5.Insmallsystems,lime pHofwater The normal . calciumcarbonateand,ifnecessary, precipitate to water beingtreatedisraisedsufficiently In thelime-softeningprocess,pHof process work? How doesthelime-softening criteria forsofteningfacilities. mg/L orlessappeartobeacceptabledesign mg/L orlessandmagnesiumhardnessof40 of120 For mostapplications,totalhardness as follows: isclassified In general,thedegreeofhardness acceptablewaterinanotherarea. be perfectly may What maybe“hard”waterinonearea Source: Water PlantDesign,1998. Treatment adesmg/LasCaCO Hardness ad150to300 Above300 0to75 75to150 Very hard Hard Moderate Soft may be used to remove carbondioxide may beusedtoremove

3

○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ plants treating high turbidity surface waters. highturbiditysurface plants treating Presedimentation problem. manganese; cloggingoftheaerationtrayisa and 10 mg/Lorless.Aerationalsooxidizesiron thecarbondioxidelevelto used andmayreduce Where CaO is 100 percent pure,CO CaOis100percent Where (mg/L) +magnesiumhardnessX] expressed as CaCO expressed 70 mg/landisoftenestimated at50mg/L itistypicallyintherangeof 30to relationship: solubility themagnesiumhydroxide from excessalkalinitycanbedetermined Desired by softening,andnottheamountpresent. shownistheamounttoberemoved hardness alkalinity inmg/LasCaCO calcium carbonatedepositswithinthefilters. of excess limeinthefilterbedsandformation inprecipitationor softening plantcouldresult softened waterpriortofiltrationatalime pHin tomaintain theproper calibrated. Failure must knowthatthepHmeterisproperly ment ofpHmustbeaccurate,andtheoperator understand limesofteningchemistry.Measure- application. Inaddition,plantoperatorsmust and linescarryinglimeslurrytothepointof the operationandmaintenanceoflimefeeders aspectsoflimesofteningis One ofthedifficult purposes, aswelltomanagefilteroperation. waterforcompliance surface the plantstreating waterturbiditymonitoringisneededat filtered groundwater.for plantstreating Inaddition, andalkalinity ofpH,hardness, measurement shouldfocuson monitoring requirements waterorgroundwater.water issurface Process softening plantsdependonwhetherthesource forlime Regulatory monitoringrequirements operating requirements? What arethemonitoringand CaO (lb/milgal)=10.6CO using inthefollowingequation: andmagnesiumcanbecalculated ate hardness toremovecarbon- The amountoflimerequired requirements? What arethechemical CaCO pressed asCO pressed 3 , and X is the required excesshydroxide , andXistherequired 2 , alkalinityisexpressedas 3 is usedprimarilybythose . EIGHT•June 1998 2 (mg/L)+4.7[alkalinity 3 . Themagnesium 2 isex- PAGE three OF FOUR cysts. Giardia Lamblia many years without any serious difficulty. In areas where there are abandoned coal-strip mines, pumping Ultimate disposal of lime or caustic possible to dispose of the sludge for the sludge into these areas may be a mines are available nearby, it may be logical and convenient solution. If acid quarries, sand and gravel pits, or coal quarries, sand and gravel pits, or or streams. Where abandoned stone ing any wastes—liquid or solid—into rivers ing any wastes—liquid or solid—into waters are leaching out of the mine into the watershed, as many such mines do, the waste sludge can help in abating serious stream pollution by neutralizing the algal growths in basins, (TOC), carbon reducing organic total the hardnessconjunction with precipitation process, controluseful for corrosion under some conditions, and acid water. Such neutralization may offer a acid water. Selection of lime, lime-soda ash, or caustic cost to the state. • removing compounds and certain organic • removing silica and fluoride, • removing iron and manganese, • reducing turbidity of surface waters in • increasing Index, the Langelier Saturation • possibly removes • removing and 228, 226 radium • removing arsenic and uranium, • removing heavy metals, • and reducing disinfection supplementing great potential savings in material treatment soda precipitationchemical process must adequately address the disposal of generated adequately sludges. What about lime softening What residuals? or small, are All plants, large now required to refrain from directly discharg- Are there concerns about soft Are there water? relativelyIn most cases, for consumer use, soft have it does water is preferable; however, soft water several disadvantages. Excessively can cause corrosion in pipes. This corrosion can household shorten the service life of pipes and appliances and can result in toxic materials, dissolved in such as lead and cadmium, being to soften a water The decision drinking water. community. supply depends completely on the Drinking water regulations do not generally require softening.

○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ ○○○○○○○○ , mg/L 3 forming tendencies, agents, • reducing dissolved minerals and scale- • reducing consumption of household cleaning 0–60 61–120 121–180 181–250 251–2846 NATIONAL DRINKING WATER CLEARINGHOUSE DRINKING WATER NATIONAL What are the benefits of are the benefits What softening? at a central Potential benefits of softening plant include the following: The selection of lime, lime-soda ash, or caustic of lime, lime-soda The selection cost, total dissolved is based on soda softening carbonate sludge production, solids criteria, hardness,and noncarbonate chemical and containing little or no stability. Water can be softened with noncarbonate hardness water with high lime alone. However, may requirenoncarbonate hardness both lime the desired finished and soda ash to achieve water hardness. with lime or lime- Softening less expensive than soda ash is generally Caustic soda softening caustic softening. increases solids of treated the total dissolved lime and lime-soda ash softening while water, dissolved solids. Caustic often decrease total soda softening produces lime less sludge than soda does and lime-soda ash softening. Caustic hydrated not deteriorate during storage, while water lime may absorb carbon dioxide and slake in during storage, and quicklime may storage causing feeding problems. The final water selection is generally based on cost, quality, and owner and operator preference. What are other softening other are What alternatives? Hardness as CaCO Courtesy of the U.S. Geological Survey, Report 78-200 Geological Survey, Courtesy of the U.S. Figure 1: Average Water Hardness in the Figure 1: Average Water Continental United States four

PAGE OF FOUR Kendall/Hunt Publishing Company. National LimeAssociation. Arlington,VA 22203. and Treatment. (1) Pizzi,NicholasG.1995. thefollowingsources: obtained from inthisfactsheetwasprimarily Information information? more Where can Ifind of mostagriculturallimingmaterials. has aneutralizingvalueforsoilacidsinexcess It source oflimingmaterialforfarmers. effective an andprovides of magnesiumhydroxide calcium carbonatewithvaryingsmallamounts of softening sludgeisgenerallyapuresource adesirablepHforplantgrowth,lime- providing too lowforoptimalplantgrowth.Inadditionto thesoilpHis fieldswhere the sludgeonfarm istouselandapplicationof area in afarming An attractivemethodforawaterplantlocated employed. increasingly other methodsarebeing land costs.Therefore, due tothedearthofavailablelandandsoaring common practices,isbecominglessfrequent disposal, sincelagooning,oneofthemost ingenuityisnecessaryforsludge Increasing of thesludge. theother,ing from inbetterdrying oftenresult filling fromoneendandwithdrawingordecant- lagoons usedonafillandletdrysequence,or million gallonsperday(MGD).Also,multiple feet per100mg/Lhardnessremovedforevery 0.5 to1.0acre- quirement willbeapproximately contentinlagoons,theannualre- moisture 50percent sludge canbedriedtoapproximately Lagooning isanotherpracticalsolution.Ifthe this methodhasbeenphasedoutinmostcases. sewersystem,although the community’sstorm todischargedirectlyinto permitted plants are wastes enteringthesamesystem.Afewsmall beneficialinneutralizingotheracidtrade prove instances, thedischarge ofsuchsludgecould Inother at leastinthevolumeproduced. systems canaccommodatethisalkalinewaste, municipal sewagedepartment,sincenotall ofthe charge mustbedonewiththeapproval a community’ssewagesystem.Suchdis- into In somecases,sludgeisdischarged directly application. to sanitarysewers,dryinglagoons,andland sludges now includes options,suchasdischarge Twelfth Edition byBulletin211.

Hoover’sWater Supply

○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ Tech Brief:Lime Softening Tech Brief:Management ofWaterTech Treatment Brief:Package Plants, Tech Brief:OrganicsRemoval, Tech Brief:IonExchangeandDemineralization, Tech Brief:CorrosionControl, Tech Brief:Filtration, Tech Brief:Disinfection, Tech via e-mailat http://www.ndwc.wvu.edu. Briefsfrom ourWebmay downloadTech siteat from theNDWCatabovenumbersoryou Brieffactsheetsarecopies ofTech available 624-8301 or(304)293-4191.Additionalfree calltheNDWCat(800) For furtherinformation, thecountry. at smallwatersystemsaround abouttechnologiesinuse contains information databasethat isapublicreference (RESULTS) forSmallSystems Technologies Treatment (NDWC) RegistryofEquipmentSuppliers Also, theNationalDrinkingWater Clearinghouse NewYork,Press. NY. Water Processes: SimpleOptions. Treatment (8) Vigneswaran, S.,C.Visvanathan. 1995. New York, NY. Water PlantDesign. Treatment American SocietyofCivilEngineers.1998. (7) AmericanWater Works Association and of CommunityWater Supplies. 1990. (6) AmericanWater Works Association. R-95/008. Handbook,U.S.EPA/625/ Transfer Technology Reports onEngineeringPracticeN0.88,AWWA Association ofCivilEngineersManualsand of Water PlantResiduals. Treatment (5) Washington D.C. Small Communities ImprovingFrom EveryTap: Water Serviceto Council.1997. (4) NationalResearch www.lime.org/. (3) NationalLimeAssociationat Practices ofWater SupplyOperations. Introduction toWater Principlesand Treatment. (2) AmericanWater Works Association.1984. Technology Transfer Handbook:Management Transfer Technology Plant Residuals, item #DWBLPE56 Water AHandbook QualityandTreatment: [email protected]. . NationalAcademyPress. item #DWBLPE65 item #DWBLPE50 EIGHT•June 1998 item #DWBLPE47 , item#DWBLPE67 item #DWBLPE63 You mayalsoorder FourthEdition. McGraw-Hill. item #DWBLPE52 item #DWBLPE59 http:// American Safe Water CRC